\[ y(x)^3 y''(x)-a=0 \] ✓ Mathematica : cpu = 1.91147 (sec), leaf count = 58
\[\left \{\left \{y(x)\to -\frac {\sqrt {a+c_1^2 \left (c_2+x\right ){}^2}}{\sqrt {c_1}}\right \},\left \{y(x)\to \frac {\sqrt {a+c_1^2 \left (c_2+x\right ){}^2}}{\sqrt {c_1}}\right \}\right \}\]
✓ Maple : cpu = 0.155 (sec), leaf count = 46
\[ \left \{ y \left ( x \right ) ={\frac {1}{{\it \_C1}}\sqrt { \left ( \left ( {\it \_C2}+x \right ) ^{2}{{\it \_C1}}^{2}+a \right ) {\it \_C1}}},y \left ( x \right ) =-{\frac {1}{{\it \_C1}}\sqrt { \left ( \left ( {\it \_C2}+x \right ) ^{2}{{\it \_C1}}^{2}+a \right ) {\it \_C1}}} \right \} \]